The invention relates to a method for folding sheets of paper and to an apparatus for folding sheets of paper.
In U.S. Pat. No. 5,490,829, a method and apparatus for folding a sheet are described in which a sheet to be folded is supplied via a nip between a pair of transport rollers and through a gap between a pair of pivotally suspended guides. When a leading portion of the sheets has arrived between a pair of folding rollers downstream of the guides, the folding rollers are stopped and the guides are pivoted while the transport rollers supply the paper over some further distance. This causes the sheet to buckle and results in a loop in the sheet.
Next, the guides are swung back, whereby transport rollers arranged on the guides clamp the sheet against the one of the folding rollers that is situated on the side of the folding gap where also the loop has been formed and where the guides had been swung to. By proceeding to drive both the folding rollers and the transport rollers, a bend in the sheet is urged between the folding rollers, whereby a first fold is formed. Thereupon, the loop together with the rest of the sheet also passes through the folding gap, in which the trailing end of the loop is pressed flat, so that a second fold is formed. Thus, with a single folding gap, two folds are formed.